Phosphorus Ultra Low Range Colorimeter HI736 Hanna Checker - Marine Water

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  • BRStv Investigates: Which is better, Hanna Phosphate or Phosphorus Checker?

Phosphorus Ultra Low Range Colorimeter HI736 Hanna Checker - Marine Water

83% Recommend this to a friend (19 of 23)

SKU: 208630
In Stock: 235
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Quick Overview

Monitoring phosphorus concentration in saltwater is important because it can cause corrosion if levels are too high. The Hanna HI736 Checker HC Handheld Colorimeter for Phosphorus ULR bridges the gap between simple chemical test kits and professional instrumentation. Accurate, affordable and easy to use. First, zero the instrument with your water sample. Next, add the reagents. Last, place the vial into the Hanna Phosphorus Checker, press the button and read the results. Done.

Full Details

Hanna Checker Phosphorus Ultra Low Range Manufacturer's Manual

Hanna Checker Phosphorus Ultra Low Range Manufacturer's Literature


  • Easier to use and more accurate than chemical test kits
  • Large, easy to read digits Auto shut-off
  • Dedicated to a single parameter
  • Designed to work with HANNA's reagents
  • Uses 10 mL glass cuvettes
  • Small Size, Big Convenience
  • Fits in the palm of your hand


  • Range: 0 to 200 ppb
  • Resolution: 1 ppb
  • Accuracy: ±5 ppb ±5% of reading
  • Light Source: LED @ 525 nm
  • Light Detector: Silicon photocell
  • Environment: 0 to 50°C (32 to 122°F); RH max 95% non-condensing
  • Battery Type: (1) 1.5V AAA
  • Auto-off: After 2 minutes of non-use and 10 seconds after reading
  • Dimensions: 81.5 x 61 x 37.5 mm (3.2 x 2.4 x 1.5")
  • Weight: 64 g (2.25 oz.)
  • Method: Adaptation of Standard Method for Examination of Water and Wastewater, 20th edition, Ascorbic Acid method


Items 1 to 12 of 23 total

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  • VERY accurate, but tricky to use at first By Randall on 8/9/2017

    Over the past couple of months, I've purchased and evaluated most of the hobbyist-level marine test kits from Red Sea, Salifert, Elos, Hanna, Nyos, SeaChem, Giesemann, Lamotte, and Hach, and then compared them to results from simultaneous water samples sent to Triton Labs for spectroscopy.

    This colorimeter is hands down the most sensitive and most accurate hobbyist device for measuring phosphorus, at least at low levels. For example, it will give me a reading of 7 when a corresponding sample sent to Triton Labs comes back as 6. Hanna's very similar phosphate colorimeter for some reason is not quite as sensitive, sometimes reading zero when there is actually a very small amount of phosphate present.

    Aside: This device measures phosphorus in ppb. A rough conversion to the phosphate we're mostly more familiar with is easy to do in your head. Multiply by 3 and move the decimal point 3 places. So, a phosphorus reading of 10 is a phosphate of .03, a reading of 20 is phosphate .06, and so on.

    Unfortunately some features of this device seem designed for people to fail to perform the test properly, requiring repeat with use of more reagents (Hanna is stingy with reagents in general). Some of these have been mentioned by another reviewer, but here are my tips to doing the test correctly every single time.

    1. Open the reagent packet first. Tamp it down, tear across the mid portion, then open one seam. You've made a little dispenser out of it. Put it aside.

    2. (Optional) Buy some small plastic perfume funnels off Amazon. They will let you quickly pour the powdery reagent into the small mouth of the test cuvette, ensuring that none is lost. They are also useful for some other Hanna colorimeters.

    3. Make sure there are NO tiny bubbles on the inside of the test cuvette, or smudges on the outside, any time it goes inside the colorimeter.

    4. After doing the blank, remove the cuvette and add the reagent (with the funnel) promptly. Cap it and shake it fairly vigorously for 90 seconds, not 2 minutes as the instructions say. Make sure there is no floating particulate matter visible when you put it back in the device.

    5. Remember to HOLD the button for the 3 minute timer; if you just press and release, you screwed up and have to repeat the test. Whether you use the built-in timer or not, set a separate timer for 3 minutes, because the built-in one makes no sound when it expires and runs the test, and the device will then turn itself off a few minutes after that. Super easy to miss if you're doing other stuff (like, oh, running other tests).
  • Times Out Too Soon By Jeffrey on 8/6/2017

    I can't believe they created a product that doesn't allow sufficient time to preform the test. I have to use two vials or it shuts off after shaking for two minutes. Poor.
  • Good but could use improvement. By Christina on 7/21/2017

    So I got this checker a few months ago and use it every water change to keep my GFO in check. I aim to keep phosphates between 0.02-0.09. I should probably always lower but it seems to do fine in that range.

    So ... I like how sensitive the checker is and either I can figure the conversion or I can plug it into apex and it will do it for me.

    A few pointers and things I'm not thrilled about. First, I use the same vial for accuracy purposes. If you do this also, you'll want to prepare your water and packet BEFORE you even start otherwise it will time out on you after you do the baseline test. So once you do the baseline and it is waiting for the second reading, there are only 3 minutes before it times out and shuts off. There is no warning for this either. I suggest setting a timer as soon as it goes to 2 so you can pour the powder and mix for the required 2 minutes without running out of time. I also suggest once you hold the button for 2 until it starts the countdown that you again set your timer for 3 minutes because it doesn't alert you to the reading and again will time out after so long and shut off. If you miss the reading you have to do the test over. I tend to multitask while I wait for the reading and if I don't have an alarm I'll completely miss it.

    Recommendations to Hanna ... give more time to prepare and mix the reagent before shutting off and maybe add a beep or something to the end so you are less likely to miss the readout. Otherwise, great product and I'll be purchasing more Hanna checkers in the future.
  • Phosphorus UL Range Hanna Checker By Rafaylina on 7/12/2017

    Really easy to do and very accurate..
  • Not consistent By KENNETH on 7/3/2017

    I have performed same test and sometimes the inconsistencies are pretty high, ranging from 25 to 80.
  • Test-retest reliability frustrating, but really the kit to have By jmfugett on 5/7/2017

    I use Hanna ULR and Red Sea PO4 kits. I use them both at times to verify results. The Hanna is very satisfying as it gives you a very refined number. The only problem is if you test 3 (4,5,6 or whatever) times you will get as many different results. Sometimes the swings are pretty severe. I have had results that run from 3 to 22 between two tests. If you can get past the fact that this colorimeter is trying to discriminate between very tiny amounts of phosphorus you won't feel as crazy about the swings. I have been using the Hanna ULR for over a year and as my PO4 levels decreased to at or near 0 and my experience and routine for taking tests have improved, the swings are not as bad and less of an issue. If testing for PO4 is important to you, you really need to get this colorimeter.
  • Best Option, But Nowhere Near Perfect By Patrick on 5/5/2017

    Seems to work okay. My main problem is with the device itself and the manufacturer's instructions.

    First, after you zero the meter, you have to add the powder to the vial and shake gently for two minutes. But, the meter shuts off after 3 minutes of inactivity. If you don't prep the powder and get it all ready to pour before zeroing, your meter will turn off before the two minutes of shake time is up. Then, since you use the same vial to zero and read, you have to start over, and you've wasted the test reagent. Seriously Hanna? You say the unit will test at least five thousand times before needing a new battery. If you test phosphates EVERY SINGLE DAY, this means the battery will last over thirteen years. If you test once a week, the battery will last 96 years. Once a month? You'll be able to use a single battery for 416 years. Now quite obviously, that's ridiculous.. batteries lose their charge naturally over time, so the battery in your checker is likely to die of natural causes before you wear it out via testing. So that begs the question, why is it so important to shut the meter off after 3 minutes of inactivity DURING YOUR TESTING PROCEDURE?! Why not bump it up to 5 minutes? Or even 10? Give me a worse case scenario... battery usage doubles and you only get 2,500 readings out of a battery? The battery will still die naturally before you wear it out with testing.

    Second, the instructions are terrible. If you're going to give us only a minute of breathing room during the testing procedure, why not tell us this so we can prepare the reagent beforehand? If you watch Youtube videos or read forum posts about this checker, you'll learn this pretty quickly. But why not put it in the instructions? This leads me to question all the other directions as well. You say "shake gently" for two minutes. Well, how vigorously is "gently?" I still have some undissolved powder shaking around in the vial after two minutes. Is this normal? Am I not shaking hard enough?

    $50 is a lot to spend on a test kit. I don't mind if the procedure is complicated, just tell me how to use the device properly. I don't want to pay $50 to have to figure things out on my own.
  • Phosphorus Hanna checker By Rafaylin on 5/3/2017

    Awesome phosphorus Hanna checker works really good highly recommended for the ultra-low phosphate..
  • Best Option Out There By Forsaken77 on 2/26/2017

    Unfortunately this is the best option out there for measuring low range phosphates. For those that don't know, you take the sample reading, multiply by 3.066, then divide by 1,000. This will give you phosphates in ppm. The reason you always get slightly different readings is because it's reading in ppb, which is a VERY low range to begin with and the meter has a +/- percent of accuracy because of the ultra low range.

    The problem, like others have stated, is getting ALL of the reagent into the vile even if you do it perfectly. You have to flick it all in one corner of the packet and some gets stuck in the corner. So by tapping on the packet to get it in the very tiny vile, you end up spilling a bit.

    Then, it says to shake for 2 minutes before putting the vile back in for the reading, but according to the instructions, the meter automatically shuts off after 2 minutes. Figure that one out. I haven't tested if it gives you the time to shake for 2 minutes and then will shut off 2 minutes after that, but I usually shake for 1 minute 50 seconds so I have time to wipe the vial clean and get it in the colorometer quick enough to hold the button down for its 3 minute countdown to let things settle.

    I wish there was a simple monitor with a probe that just constantly measured phosphates and nitrates. It seems these are the only 2 parameters that can't be monitored,yet they are some of the most important factors in determining algae issues.

  • Hanna H1736 By Bori on 1/22/2017

    Great and simple! Nothing more to be said about this item!
  • Great product By Paul on 10/2/2016

    This has been a great device for determining phosphate levels in a reef tank. Easy to use once you get used to the procedure. Number readout and no guessing colors.
  • It really is easy By Aaron on 7/18/2016

    I was hesitant to grab this because of a few reviews that stated it was difficult to get all of the reagent in the curvet but if you flick the packet a couple of times to get the reagent down to the bottom corner, cut the packet like instructed, and fold/roll one side to create a half funnel, it just couldn't be any easier.


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Product Questions

Which checker should I use for a reeftank the hi713 or hi736 to check for phosphate?
Question by: John on May 28, 2016 11:19:00 AM
Great question!
We use the Hi713 in most cases as it is easier to use and read over the phosphorus which requires additional calculation to convert to phosphate.
Answer by: Connor (Admin) on Jun 3, 2016 1:35:00 PM